As flu season begins some respiratory illness sufferers are turning to 'salt caves' for relief, but the Lung Foundation is warning against the trend.

Salt therapy is an alternative health practice that has been around for hundreds of years, but has grown in popularity in Australia since the opening of the country's first replica 'salt caves' about 10 years ago.

Marshal Rubinstein opened a 'salt cave' last month in the northern New South Wales town of Byron Bay.

He said he began researching salt therapy after he attended a session in Sydney and found significant relief from a bout of bronchitis.